The 60th Anniversary of the Tuya: a BC perspective
J.K. Russell (Volcanology & Petrology Laboratory, Earth & Ocean Sciences, University
of British Columbia, Vancouver, Canada, ph: 1-604-822-2703, fax: 1-604-822-6088, email krussell@eos.ubc.ca); B.R. Edwards (Department of Environmental Science,
University of East Anglia, Norwich, Great Britain); K.A. Simpson (Geological Survey of
Canada, Vancouver, Canada).
Sixty years ago, W.H. Matthews published a series of landmark papers describing
the stratigraphy and morphology of basaltic volcanoes in the Tuya-Teslin region of
northwestern British Columbia [1, 2]. There, he encountered numerous, small, apparently
young, volcanic edifices hosting a variety of enigmatic features. Most of the volcanoes
are basaltic in composition but are steep-sided and commonly have “flat” tops. Later
Mathews recognized that these volcanic edifices shared common stratigraphic elements,
including: pillow lavas and breccias, massive to bedded deposits of fragmented glassy
basalt (hyaloclastite), and capping massive basalt lava. He proposed the term ‘tuya’ for
these volcanoes and interpreted their morphology and attendant volcanic lithofacies as
indicative of volcanic eruptions from beneath and within late Pleistocene glacial ice
sheets
Recent research shows that the Tuya Region tuyas are part of the northern
Cordilleran volcanic province (NCVP), a region of extension-related mafic alkaline
magmatism that was active when the Cordilleran Ice Sheet (CIS) inundated the
Cordillera. Modern studies of five tuyas (Mathews Tuya, Tuya Butte, South Tuya, Ash
Mountain, Blackfly tuya) show that the stratigraphy at each centre is unique but all show
evidence that eruption, transport and deposition of volcanic deposits transitioned from
being entirely subaqueous to entirely subaerial, resulting in a morphology and
stratigraphy consistent with the classic “tuya” formation. Recognising the transition from
subaqueous to subaerial volcanism at multiple volcanic centres provides constraints on
regional water depth and by association ice thickness. Volcano morphology likely reflects
primary differences in eruptive style in the latter subaerial stages of volcanism (explosive
vs effusive).
Mathews later pioneering work [3, 4, 5] involved volcanic deposits in the Garibaldi
volcanic belt (GVB) (e.g., Canadian Cascades). This work provided a first description of
an andesitic tuya and identified a variety of morphologies (esker-confined lavas),
structures (vertical lava fronts) and features (horizontal and radiating patterns of
columns) indicative of ice-contact volcanism. The recent work of Kelman et al. [6] at
Mount Cayley has shown the GVB to have a distinctive expression of glaciovolcanism.
The Mount Cayley volcanic field is situated at high elevation and in very high relief and,
thus, the ice masses associated with most eruptions were probably relatively thin and
highly permeable, promoting meltwater escape. This has resulted in glaciovolcanic
landforms, which are virtually devoid of pillows and hyaloclastite. The strongest
evidence for glaciovolcanic events is the occurrence of: a) flow-dominated tuyas (e.g.,
Table; [3]); b) steep to vertical walls of lavas perched on valley walls at high elevations,
and c) the pervasive presence of intense columnar jointing oriented horizontally or in
radiating masses.
The linkages between glaciation and volcanism in the BC cordillera were first
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explored by Grove [7]. He posed the question whether unloading of the crustal
lithosphere triggered the onset of volcanism. Edwards and Russell [8] reviewed this
question and argued that the age-relationships between volcanism and glacial loading and
unloading events are not sufficiently well known to test this idea in a meaningful way.
The question of coupling between glaciation and cordilleran volcanism remains one of
the seminal issues in the Canadian cordillera. The answer will require a concerted effort
at obtaining ages for both volcanic and glacial deposits.
References
[1] Watson, K.D., Mathews, W.H. 1944. The Tuya-Teslin Area, Northern British Columbia,
British Columbia Department of Mines, Bulletin 19, 52 pp.
[2] Mathews, W.H. 1947. ‘‘Tuyas,’’ flat-topped volcanoes in northern BC. Am J Sci 245, 560–
570.
[3] Mathews, W.H. 1951. The Table, a flat-topped volcano in southern BC. Am J Sci 249, 830–
841.
[4] Mathews, W.H. 1952. Mt Garibaldi, a supraglacial Pleistocene volcano in SW BC. Am J Sci
250, 81–103.
[5] Mathews, W.H. 1958. Geology of the Mount Garibaldi map-area, southwestern British
Columbia, Canada: Part II. Geomorphology and Quaternary volcanic rocks. Geol Soc Am
Bull 69, 179–198.
[6] Kelman, M.C., Russell, J.K., and Hickson, C.J. 2002. Effusive intermediate glaciovolcanism
in the Garibaldi Volcanic Belt, SW BC. In: Smellie, J.L., & Chapman, M.G. (eds.) VolcanoIce Interaction on Earth & Mars. Geol Soc Lond, Sp. Pub, 202, 195-211.
[7] Grove, E.W., 1974. Deglaciation — a possible triggering mechanism for recent volcanism.
Proc. IAVCEI, Santiago, Chile, pp. 88–97.
[8] Edwards, B.R. & Russell, J.K. 1999. The northern Cordilleran volcanic province. Geol, 27,
243-246.
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